The invention relates to a spool valve, such as oil valves and the like, incorporated into hydraulic control circuits of automatic transmissions of an automobile or the like to perform switching of oil flow passages.
Spool valves have been manufactured by machining a rod material by means of a lathe or the like, in which there are many problems. For example, there is much material discarded as chips, machining takes a long time and stress relief is essential in the case where application of heat treatment such as carburization or the like generates stress of heat treatment to distort a shaft.
To solve such problems, the inventors of the present application have devised, as disclosed in Japanese Provisional Patent Publication No. 9-264444, a spool valve, in which collars are fixed to a shaft by fitting a plurality of collars onto a shaft material in predetermined positions, and using a rolling die to reduce the shaft material at both ends of the collars in diameter to cause plastic flow of metal to form annular ridges.
However, such collars are manufactured in multi-stage processes by cold forging in a cold forging machine after shearing of a rod material to a predetermined length. It has been difficult to manufacture thin collars since in the case of manufacturing collars having a thickness as thin as, for example, 4 mm or less, a rod material cut by shearing causes deformation such as die wear or the like. Also, for the purpose of low fuel consumption in automobiles, it has been demanded to make a weight of an automobile as small as possible. Such collars involve, in addition to a problem that being a ring-shaped solid body, they are heavy, problems that provision of oil drain holes necessitates boring by a drill, which takes time and man-hour and the manufacturing cost is increased by waste of a material caused by punching a central hole in a rod material, which allows fitting onto a shaft.
The invention has been devised to solve the above mentioned problems of the prior art and enable manufacturing collars having a small thickness and to provide a spool valve provided with collars, which are lightweight and high in yield of material.
A spool valve according to the invention has a plurality of small-diameter portions formed at predetermined spacings on a peripheral surface of a shaft, and pairs of annular ridges on peripheral surfaces of the small-diameter portions to have a larger diameter than an inner diameter of collars, the collars being closely fitted between the annular ridges to make valve bodies, characterized in that the collars comprise an inner wall, an outer wall and at least one connection therebetween, the at least one connection is formed of the same material as that of the inner wall and outer wall, and connects the inner wall and the outer wall integrally to each other at predetermined positions on the inner wall and the outer wall, and an annular gap is provided between the inner wall and the outer wall. In addition, the collars can be used which are formed with oil drain holes, as desired.
Also, A method for manufacturing a spool valve, according to the invention, comprises the steps of: fitting onto a shaft material and aligning in predetermined positions a plurality of collars, which are manufactured by forming a metallic sheet and comprise an annular gap between an inner wall and an outer wall; and using a rolling die to reduce the shaft material around both ends of the respective collars in diameter to cause plastic flow of metal to form at both ends of the respective collars annular ridges having a larger diameter than an inner diameter of the collars to thereby fix the respective collars to the shaft. In addition, oil drain holes can be provided on the respective collars by punching, as desired.